Translating Nature’s Historians: The Tree Ring Lab Turns 40

Tree ring research was a young field in 1975 when Ed Cook (above, in Nepal) and Gordon Jacoby founded the Tree Ring Lab at Lamont. The Lab would become a world leader in tree ring sampling and analysis and a source of technology and training for dendrochronologists around the world. Photo by Paul Krusic

As the Lab got going in the 1970s, its scientists began developing tree ring chronologies across North America. On a talus slope near New Paltz, NY, scientists found old, undisturbed hemlock trees that contributed to a 400-year record of drought variability in the Hudson Valley. Photo by Francesco Fiondella — As the Lab got going in the 1970s, its scientists began developing tree ring chronologies across North America. On a talus slope near New Paltz, NY, scientists found old, undisturbed hemlock trees that eventually contributed to a 400-year record of drought variability in the Hudson Valley. Photo by Francesco Fiondella

Finding old-growth trees that haven’t been disturbed by human activity often requires hiking, kayaking and camping out for days. The only way into Wrangell St. Elias National Park and Preserve in Alaska was by air. The team had to fly in one by one to take samples along the tree line. Photo by Nicole Davi

In Alaska, Gordon Jacoby (above), Rosanne D’Arrigo, Greg Wiles, and Nicole Davi \used tree rings to date volcanic eruptions and earthquakes. The Lab was able to create a millennial-length record of climate change and volcanic eruptions there. These trees were killed by ash from Mount Churchill around 800 AD. Photo by Nicole Davi — In Alaska, Gordon Jacoby (above), Rosanne D’Arrigo, Greg Wiles, and Nicole Davi used tree rings to date volcanic eruptions and earthquakes. The Lab was able to create a millennial-length record of climate change and volcanic eruptions there. These trees were killed by ash from Mount Churchill around 800 AD. Photo by Nicole Davi

In 1989, Gordon Jacoby and Rosanne D’Arrigo (above), the Lab’s first PhD student and now associate director of the Division of Biology and Paleo-Environment, published a landmark reconstruction of temperatures dating back 300 years across North America. The records show the effects of global warming. Photo courtesy of Gordon Jacoby — In 1989, Gordon Jacoby and Rosanne D’Arrigo (above), the Lab’s first Ph.D. student and now associate director of the Division of Biology and Paleo-Environment at Lamont, published a landmark reconstruction of temperatures dating back 300 years across North America. The records showed the effects of global warming. Photo courtesy of Gordon Jacoby

Tree rings also hold records of earthquakes. Near Seattle, the Lab used trees killed in a landslide and fallen logs discovered in a nearby lake to confirm that a mega earthquake shook the Pacific Northwest in 1699-1700 and generated a tsunami, likely the “orphan tsunami” that reached Japan in 1700. Photo courtesy of Gordon Jacoby

Along the San Andreas fault, fallen trees near Wrightwood, California, revealed when past earthquakes caused trauma to the trees, disrupting their growth. Dead trees allow access to full cross-sections of their rings, but getting them to the lab isn’t always easy. Photo courtesy of Gordon Jacoby

In the 1980s, the Lab began work in Asia that would develop into the Monsoon Asia Drought Atlas. "Tree One" (above) was the first tree cored in Mongolia by Gordon Jacoby. As soon as he examined the core, he knew the research had potential: he could see narrow growth during the Little Ice Age in the 1800s and very rapid growth during the 20th century as temperatures rose. Photo by Rosanne D’Arrigo — In the 1980s, the Lab began work in Asia that would develop into the Monsoon Asia Drought Atlas. “Tree One” (above) was the first tree cored in Mongolia by Gordon Jacoby. As soon as he examined the core, he knew the research had potential: he could see narrow growth during the Little Ice Age in the 1800s and very rapid growth during the 20th century as temperatures rose. Photo by Rosanne D’Arrigo

In Nepal, the team found 1,200-year-old hemlock trees. To get to this site, Ed Cook (left), Paul Krusic (right) and Brendan Buckley hiked for 13 days, cored trees for five days and then walked back out. Everything they needed, from equipment to food, they had to carry. Photo courtesy of Brendan Buckley

Working in forests always carries risks, from bears in Alaska to mosquitoes in South Asia. While coring trees in Burma, the scientists had to be mindful of tigers. Photo by Paul Krusic

From the highest peaks to submerged forests, there is nowhere a tree ring scientist won't go. Brendan Buckley and colleagues sample trees underwater in Belize. Photo by Tony Rath — From the highest peaks to submerged forests, there is nowhere a tree ring scientist won’t go. Brendan Buckley and colleagues sample trees underwater in Belize. Photo by Tony Rath

The Lab’s tree ring work in the U.S. Southwest documents a history of drought. Ed Cook (above) published a landmark paper in 2004 describing past mega droughts that extended for hundreds of years. Later work with the bristlecone pines tracked 1,100 years of El Nino/La Nina fluctuations. Photo by Paul Krusic — The Lab’s tree ring work in the U.S. Southwest documents a history of drought. Ed Cook (above) published a landmark paper in 2004 describing past mega droughts that extended for hundreds of years. Later work with bristlecone pines tracked 1,100 years of El Nino/La Nina fluctuations. Photo by Paul Krusic

Tree rings reveal patterns that can impact modern economies. In Mongolia, Nicole Davi's team reconstructed 1,000 years of temperature changes, providing insight into recent warming and past volcanic activity. Ph.D. student Mukund Palat Rao and others studied the recent impact of dry summers and exceptionally cold winters on livestock survival. Photo by Gordon Jacoby — Tree rings reveal patterns that can impact modern economies. In Mongolia, Nicole Davi’s team reconstructed 1,000 years of temperature changes, providing insight into recent warming and past volcanic activity. Ph.D. student Mukund Palat Rao and others studied the recent impact of dry summers and exceptionally cold winters on livestock survival. Photo by Gordon Jacoby

Some of the Lab’s most recent work has focused on drought risk in California and tree recovery after drought. A 2015 study by Park Williams (above, shown on another project in Ethiopia) found that excess heat as temperatures warm was damaging trees’ ability to store carbon and their survival. Photo courtesy of Park Williams

Tools of the trade: Tree ring researchers use a metal increment borer to extract a pencil-thin sample from the tree, extending from the newest rings at the bark to the oldest rings at the center. The process does not cause permanent injury to the tree. Photo by Nicole Davi

At the Tree Ring Lab, the team sands and polishes the cores to bring out their anatomy. The researchers routinely sample 20 to 50 trees in the same site to compare and derive a common response from the ring widths. Photo by Nicole Davi

Researchers use pattern matching (aka skeleton plotting) and statistical analysis to assign years to each ring, called cross-dating. If the rings tell a similar story, the researchers can more confidently estimate meteorological records back to years before weather instruments existed. Photo by Nicole Davi

An important principle set by the Tree Ring Lab’s founders was to share knowledge widely and develop networks of researchers. At a tree ring field week in Mongolia, students from the National University of Mongolia learn the basics of dendrochronology. Photo by Nicole Davi

Forty years was just the beginning. Follow the Tree Ring Lab’s work and learn more about its technology and history at http://www.ldeo.columbia.edu/tree-ring-laboratory

Throughout the Tree Ring Lab at Lamont-Doherty Earth Observatory, you’ll find pencil-thin wood cores under microscopes and growth rings being measured with precision. They come from trees all over the world, and together they hold thousands of years of climate history – when major droughts set in, when the planet cooled and when it started warming, even when earthquakes rattled the landscape and volcanoes erupted.

One famous collection tracks changing temperatures and rainfall across the Northern Hemisphere, from volcanic eruptions that led to fast cooling in the early 1800s, to a warming trend that started with the Industrial Revolution and continues today. Another holds evidence used to confirm that a mega-earthquake struck the Pacific Northwest in 1699-1700, likely creating the “orphan tsunami” that reached Japan. Teak samples from South Asia reveal trends in the changing monsoon season. Bristlecone pine cores from the American Southwest hold warnings of drought.

It all started 40 years ago this month, when Ed Cook and Gordon Jacoby established the Tree Ring Lab at Lamont with a grant from the National Science Foundation.

Tree ring research was a young field, evolving from just dating wood to tracking droughts and temperature swings. The Lamont Tree Ring Lab, among the first in the world, would expand dendrochronology’s capabilities over the years and become a global leader in research, training and technology.

“Silent though they are, the trees, it turns out, can speak volumes,” Jacoby, who recently passed away, wrote in 1999. “The size, density, anatomy and chemistry of each ring reflect the environmental conditions in the year in which it grew. So like ancient scribes, long-lived trees can sensitively record the environmental history of a given place and time.”

300 Years of Climate History

Jacoby and Cook would explore the world over the Lab’s first four decades, but they started out closer to home, working in the climate-sensitive boreal forests of North America to better understand forest dynamics and the physiological impacts of climate on tree growth.

With Rosanne D’Arrigo, the Lab’s first graduate student and now director of the Division of Biology and Paleo-Environment at Lamont, they would fly into remote regions of Alaska and Canada and camp for weeks as they collected samples at the tree line, where trees are at the edge of survival, and small changes in temperature or water stress will leave measurable markings.

Gordon Jacoby cores a tree in Alaska to reconstruct temperature through history.

Back in the Lab, the team was developing new methods of analysis and software to process stable isotope ratios in tree cellulose to function as paleo-thermometers. They also turned their attention to acid rain in the 1980s, ruling out natural causes for the widespread deaths of red spruce trees across New England. At the same time, the scientists continued to build North American tree-ring chronologies.

By 1989, Jacoby and D’Arrigo were able to publish a reconstruction of temperatures across the Northern Hemisphere going back over 300 years. The tree ring data reflected a climate that had been cooler in the 1700s and early 1800s but then warmed as carbon dioxide emissions from industry and vehicles increased.

Their research was a breakthrough for climate science and dendrochronology. Earlier studies had found evidence of a warming climate in pockets, including a 1981 study by Jacoby and Cook tracking 400 years of climate change in the Yukon. The new chronology showed that that trend extended around the world.

“Prior to this study, tree-ring reconstructions of past temperatures were limited to the local and regional scale. This paper expanded those analyses to the hemisphere, which provided more relevance for interpretation of large-scale temperature trends, including recent anthropogenic warming,” D’Arrigo said.

In the 1990s, Jacoby, Cook, and D’Arrigo, along with Paul Krusic, Brendan Buckley and Nicole Davi, shifted their attention to Southeast Asia and Mongolia. Members of the team once trekked for 13 days across Nepal to sample ancient hemlocks that held a 1,200-year history of climate in the region. In Burma, they were on guard for tigers, and they risked arrest at checkpoints in politically unstable regions, but they made progress toward what would become a widely used atlas of drought in the Asian monsoon region.

Old Tools, New Technology

The tools that tree ring scientists hike in with today with aren’t much different than those used by foresters 200 years ago. Increment borers are still metal shafts best powered by human muscles that can feel changes in resistance while coring a tree.

It is in the lab where new technology, increasing computing power and new methods of analysis have advanced the field by magnitudes.

Over the years, Cook and Krusic developed widely used methods of statistical analysis and tree ring software that they posted free for anyone to use, including a computer program that remains the standard for developing tree ring chronologies, ARSTAN (autoregressive standardization). Sharing knowledge and tools remains a founding principle for the lab. As Cook explained, “We always felt it was a service we should provide to the community.”

Rose Oelkers, a technician at the Tree Ring Lab, examines a cross-section of wood under a microscope.

The lab scientists also advanced the use of technology such as X-ray densitometry to extract sensitive climate data. The team developed a low-cost, high-resolution ring-width measuring system that reduced the time to obtain accurate tree ring measurements, allowed them to increase sample analysis from hundreds to thousands and contributed to tree ring research around the world. Today, D’Arrigo, Laia Andreu Hayles, Nicole Davi and others are experimenting with blue light densitometry that measures ring density through imaging.

“The Tree Ring Lab at Lamont-Doherty has literally re-defined our knowledge of climate over the past 1,000 to 2,000 years,” said Henri Grissino-Mayer, a dendrochronology professor at the University of Tennessee whose software list for students is filled with Tree Ring Lab links. “Today, one cannot open a textbook and read about past climate without reading the accomplishments of the staff and scientists at the TRL.”

Fine-Tuning Climate Models

The advanced software and a growing network of samples and trained colleagues around the world helped the lab develop two widely used drought atlases: the Northern American Drought Atlas, published in 2004, and the Asian Monsoon Atlas, published in 2011.

The drought atlases and many of the lab’s studies have been crucial to the development of climate models.

Cook explained how his work with the long-lived, slow-growing bristlecone pines of the American Southwest first piqued the interest of climate modeler and Lamont colleague Richard Seager in the early 2000s.

In 2004, Cook showed that the ongoing drought in the U.S. Southwest paled in comparison to a drought about 1,000 years earlier. The paper suggested that the region is extremely vulnerable to disastrous drying during periods of climate warming. Seager followed with an influential 2007 paper suggesting that the region will dry significantly in the 21st century and that the transition to a long-term more arid climate may already be underway.

“We have trees in North America going back 1,000 years that show periods of incredible mega droughts. You throw on top of that the greenhouse forcing effects, and we could potentially see a phenomenally bad state of mega-drought. Whether it will happen, you can argue. Model projections suggest it could,” Cook said.

In Tasmania, Brendan Buckley and Ed Cook were able to reconstruct 4,000 years of temperature history and develop an almost complete Holocene link of more than 10,000 years.

Cook’s bristlecone pines have also helped the Lab reconstruct a 1,100-year history of El Niño Southern Oscillation fluctuations, supporting the idea that continued warming may lead to more extreme climate conditions around the globe.

The lab has turned attention more recently to the influence of climate change on drought in western North America, with Park Williams finding that warming increases forest drought stress, leading to decreased growth and decreased ability to recover after droughts. His latest paper explains how global warming is exacerbating the current drought in California, and will continue to exacerbate future droughts as warming continues.

The Tree Ring Lab has dated timbers from a ship found buried at the site of the World Trade Center; connected a warm, wet period in Mongolia to the rise of Genghis Khan; and found tree ring evidence of the 1815-1816 eruption of Tambora in Indonesia, the same period American colonists called “the year with no summer.” A recent study of tree rings from Mongolia dating back more than 1,000 years confirms that warming in central Asia has no parallel in any known record. Cook, D’Arrigo and Buckley are also pursuing tree rings in the tropics, where the lack of seasons makes annual rings more difficult to find.

Along the way, the team has helped establish dendrochronology labs in Nepal, Bhutan, Thailand, Indonesia, Tasmania, New Zealand, Mongolia and across North America.

“We have helped train young scientists, young foresters, dendrochronologists from many different countries of the world,” Cook said. “We’ve probably done more of that than any other tree ring lab in the world because we wanted a global view. We wanted to see the bigger picture beyond the work in our own back yard.”